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Developmental Biology - Increasing Egg Quality
Mouse Eggs Can Come From Granulosa Cells
Mouse pups were recently born from eggs made from granulosa cells - which typically only surround oocytes...
By introducing a chemical cocktail to granulosa cells, researchers in China induced those cells to transform into functional mouse eggs (oocytes). Once fertilized, these new eggs successfully produced healthy mouse pups, with no physical difference from sexually bred mouse pups. This chemical reprogramming method appeared December 24 in the journal Cell Reports.
Ovarian follicles are the single functional unit produced in the ovary. Follicles consist of an oocyte — the immature egg — surrounded by granulosa cells. Besides being crucial to developing follicles, studies show granulosa cells are very plastic with stem cell-like characteristics. They can become many cell types depending on cues from their surrounding environment.
"In vitro fertilization only uses oocytes for the procedure. After egg retrieval, granulosa cells in the follicle are discarded. It got us thinking, what if we can use these granulosa cells?"
"As every egg has thousands of granulosa cells surrounding it, if we can induce them into pluripotent cells and turn those cells into oocytes, aren't we killing two birds with one stone?"
Lin Liu PhD, College of Life Sciences, Nankai University, Japan and senior author.
Granulosa cells undergo cell death and differentiation when removed from the follicle. Liu and his team developed a chemical "cocktail" using Rock inhibitor and crotonic acid to create Chemically Induced Pluripotent Stem Cells (CiPSCs) from granulosa cells.
The team introduced Rock inhibitor to prevent cell death and promote proliferation. Crotonic acid facilitates stimulating granulosa cells, in combination with other chemicals, into becomming competent germline and pluripotent stem cells. These new pluripotent stem cells exhibit pluripotency similar to embryonic stem cells.
"It's a surprising result. The competency of induced pluripotent germline cells is usually lower than embryonic stem cells.
Germline competency is crucial for transfer of genetic information. With the co-formulation of Rock inhibitor and crotonic acid, it's not only more efficient but its quality increased."
Lin Liu PhD
Another cocktail of Rock inhibitor and vitamin C is introduced to germline-competent pluripotent stem cells to improve follicle development and induce meiosis. Meiosis is the process of a single cell becoming a sex cell — the egg. Germ cells and oocytes rejuvenated from granulosa cells exhibit high genomic stability and successfully produce offspring that show normal fertility.
"We can consistently manipulate the concentration and treatment time of these small chemicals. Compared to traditional methods such as transfection — which reprograms cells into somatic cells — chemical treatment gives greater control. Transfection has a higher risk of gene instability."
"This is the first time granulosa cells were turned into oocytes, a crucial development in reproductive biology."
Lin Liu PhD
However, implementing this procedure in humans has a long way to go. Liu believes the process has better prospects for preserving human fertility and endocrine function — than in treating human infertility.
Abstract Highlights
• Granulosa cells can be reprogrammed to form oocytes by chemical reprogramming
• Rock inhibition and crotonic acid facilitate the chemical induction of gPSCs from GCs or germ cells
• PGCLCs derived from gPSCs exhibit longer telomeres and therefore high genomic stability
Summary
The generation of genomically stable and functional oocytes has great potential for preserving fertility and restoring ovarian function. It remains elusive whether functional oocytes can be generated from adult female somatic cells through reprogramming to germline-competent pluripotent stem cells (gPSCs) by chemical treatment alone. Here, we show that somatic granulosa cells isolated from adult mouse ovaries can be robustly induced to generate gPSCs by a purely chemical approach, with additional Rock inhibition and critical reprogramming facilitated by crotonic sodium or acid. These gPSCs acquired high germline competency and could consistently be directed to differentiate into primordial-germ-cell-like cells and form functional oocytes that produce fertile mice. Moreover, gPSCs promoted by crotonylation and the derived germ cells exhibited longer telomeres and high genomic stability like PGCs in vivo, providing additional evidence supporting the safety and effectiveness of chemical induction, which is particularly important for germ cells in genetic inheritance.
Authors
Chenglei Tian, Linlin Liu, Xiaoying Ye, Haifeng Fu, Xiaoyan Sheng, Lingling Wang, Huasong Wang, Dai Heng and Lin Liu.
Acknowledgments
This work was supported by the National Natural Science Foundation of China and the China National Key R&D Program. The authors declare no competing interests.
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Jan 1 2020 Fetal Timeline Maternal Timeline News
Photo of a mouse made from germ cells known as gPSC4-derived oocytes (eggs). The crotonic acid added along with 1 N NaOH, adjusted the cell pH to approximately 7.0. Stage 2 of reprogramming activated 2-cell embryos to be fertilized by IVM or IVF. Now about one year old, gPSC4- mice can sexually reproduce, generating litters of pups. CREDIT Lin Liu.
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